The prediction of the location and type of mineral scale that may form around or within the production or surface facilities of an oil well is an important factor both in the design of the well and the formulation of strategies to cope with the mineral scale.
Current methods for predicting mineral scale formation involve the retrieval of samples from downhole, which are then either analysed at the surface or else sent off to laboratories for analysis. Errors and delays can arise from this ex situ analysis.
Electrochemical methods have previously been developed for the measurement of the concentration of a number of different metal ions, and some have been deployed in shallow boreholes, lakes and ocean waters. However, the application of these methods to oilfield operations has been limited, as the high temperatures (up to 175 Celsius) and pressures (up to 1500 bar) common to most reservoirs, make their use impractical. Furthermore, many electrochemical methods are not able to distinguish between the principal metal ions (Ca2+, Ba2+ and Sr2+} responsible for scale formation. This problem is compounded by the low concentrations of these ions (about 10 s mg/L) in formation water which is often highly saline.
The ability to rapidly and conveniently distinguish scaling ions may also find application, for example, in fingerprinting waters flowing into a hydrocarbon well from different producing zones. This information, which is indicative of connectivity between different zones of a producing well, may allow the optimization of production strategies for recovering the oil in place.